Rollins said he was warming up as usual before Monday's home opener against Washington when he felt what he thought was a cramp in his calf. As he tried to push through the exercises, he said he thought he might have torn something.
An MRI on Tuesday revealed a Grade 1 or 2 strain. Rollins already said the leg has felt better since Monday.
"It's a lot better than I thought it might be," Rollins said. "Initially it was like I could hear [a tear] happened. I could feel it."
The Phils decided to play this on the cautious side, considering how early it is in the season and how other players on the team have dealt with similar calf injuries.
Utility man Greg Dobbs suffered from calf injuries last season that hampered him. Center fielder Shane Victorino had calf injuries in 2007 and '08.
Rollins said Victorino told him to take his time with this one.
"Obviously when Jimmy goes, we go," general manager Ruben Amaro said. "But one of the beauties of our club is we have a pretty resilient group. We've lost guys in the past and we've adjusted around them."
The Phillies called up infielder Wilson Valdez to replace Rollins on the 25-man roster. Valdez, a six-year veteran, spent last season with the Mets and made 23 starts.
Juan Castro started Monday and Wednesday at shortstop.
"We've got guys that can come play hard," manager Charlie Manuel said. "I think we'll be fine. That's part of what you go through."
It's just the second career stint on the disabled list for Rollins. He missed a month in 2008 with an ankle sprain.
"I figured he'd miss some time," Manuel said. "I did it a couple of times, I know how it feels. It requires some rest."
On the positive side for Philadelphia, right fielder Jayson Werth's hip flexor injury won't cause him to miss any time. Though out of the lineup Wednesday, Werth took batting practice and was available to pinch-hit, according to Manuel.